1. Field of the Invention
The present invention relates to a component having a micromechanical microphone structure which is implemented in a layered structure on a semiconductor substrate. The microphone structure includes a diaphragm structure having an acoustically active diaphragm which at least partially spans a sound opening in the back side of the substrate. The diaphragm is provided with a movable electrode of a microphone capacitor. In addition, openings are provided in the diaphragm structure, via which pressure compensation occurs between the back side and the front side of the diaphragm. Moreover, the microphone structure includes a stationary acoustically permeable counterelement having vents, which is situated in the layered structure above the diaphragm and which functions as a carrier for a nonmovable electrode of the microphone capacitor.
2. Description of the Related Art
The diaphragm of the type described above is acted on by sound via the sound opening in the substrate and/or via through openings in the counterelement. The resulting diaphragm deflections are detected as fluctuations in the capacitance of the microphone capacitor.
However, the diaphragm structure responds not only to sound pressure, but also to fluctuations in the ambient pressure and to pressure fluctuations caused by air flow, for example from wind. These types of interfering influences on the microphone signal may be reduced by a slow pressure compensation between the two sides of the diaphragm. This pressure compensation takes place via flow paths between the vents in the counterelement and the sound opening. The speed of such a pressure compensation depends essentially on the flow resistance of the flow paths. The smaller the flow resistance, the more quickly a pressure compensation between the front side and the back side of the diaphragm is completed, and the less influence atmospheric pressure fluctuations and air flows have on the microphone signal. However, the sensitivity of the microphone to low-frequency acoustic signals is also reduced. In addition, the pressure on the diaphragm due to thermal noise increases.
The flow resistance during the pressure compensation between the front side and the back side of the diaphragm should thus be adjusted according to the sought frequency range of the microphone component.
A microphone component of the type mentioned at the outset is described in U.S. Pat. No. 6,535,460 B2. The design of this microphone component includes a substrate having a through opening which functions as a sound opening and is spanned by a diaphragm. A perforated counterelement is situated above the diaphragm and at a distance therefrom, and is connected to the substrate at the edge area of the sound opening. The diaphragm and counterelement together form a microphone capacitor, the diaphragm functioning as a movable electrode, while the stationary counterelement is provided with a rigid counter electrode.
In the known microphone component, a ring-shaped support structure for the diaphragm is provided above the edge area of the sound opening, at the underside of the stationary counterelement facing the diaphragm, which is used for the acoustic seal. For this purpose, the diaphragm is electrostatically attracted to the support structure. Although the perforation openings in the counterelement closest to the support structure also contribute to the pressure compensation between the front side and the back side of the diaphragm, the pressure compensation here occurs primarily via openings in the counterelement and in the diaphragm structure which are situated outside the area surrounded by the support structure, and which together with the air gap between the counterelement, the diaphragm structure, and the substrate form a flow path to the sound opening. The flow resistance is a function, on the one hand, of the distance between the pressure compensation openings and the acoustic seal, and on the other hand, of the width of the gap between the counterelement, the diaphragm structure, and the substrate. Manufacturing-related tolerances in the gap width frequently occur in a range which greatly influences the flow resistance.